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Tracer-Guided Characterization of Dominant Pore Networks and Implications for Permeability and Wettability in Shale


Tracer-Guided Characterization of Dominant Pore Networks and Implications for Permeability and Wettability in Shale

Sheng Peng*1, Robert M. Reed1, Xianghui Xiao2

1. Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at

Austin, University Station, Box X, Austin, Texas 78713, USA

2. Advanced Photon Source, Argonne National Laboratory, Lemont, IL 60439, USA

Abstract: Pore network characterization is an important aspect in unconventional reservoir evaluation. A common technique is using the scanning electron microscope (SEM). While application of this technique brings substantial advances in pore characterization in shales, understanding the connected pore network that dominates flow in shale samples is limited by using SEM alone because of small fields-of-view and lack of views of connectivity in 3D. In this research, a new technique integrating tracer imbibition, micro-CT imaging, and SEM imaging was developed to provide a “real” solution for multiscale imaging in shale. Tracer imbibition indicates pore connectivity; micro-CT imaging after tracer imbibition thus provides an overview of the connected pore network at the millimeter scale. With guidance from micro-CT images after tracer imbibition, a more accurate and detailed characterization of pore systems and related mineralogy can be conducted using higher-resolution SEM. Therefore, this integrated method provides a way of simultaneous viewing of the overall framework of the dominant pore network and details of the pores. The method was applied to five samples from Wolfcamp and Eagle Ford Formations. Results reveal the effectiveness of the new method by showing different patterns of distribution of the dominant pore network and different controlling mineralogy. Dominant porosity, estimated from grayscale analyses, displays a good correlation with permeability. This result indicates that dominant porosity is more relevant to permeability than total porosity. Results from imbibition tests and micro-CT imaging are compared with that from contact angle measurement. Important implication for wettability can be obtained from the comparison. Contact angle measurements characterize the surface wettability and the results are consistent with the imbibition behavior in microfractures, whereas local pore wettability is more complicated and is affected by local surrounding mineral phases or organic matter.